•Both LM and BM present outstanding HCF strength, 652MPa and 656MPa, respectively.•Prismatic slip lines, dislocation tangles and twins can be found in fatigued specimens.•Microcracks mainly initiate ...at GB α films or at αs/βr interphases in LM.•Microcracks primarily nucleate at αp/βtrans interfaces and at αp particles interiors in BM.•Fatigue cracks growth with a rough path results from fine and local basket-weave αs lamellae.
High-cycle fatigue (HCF) behavior of Ti–5Al–5Mo–5V–3Cr–1Zr (Ti-55531) alloy with both lamellar microstructure (LM) and bimodal microstructure (BM) was studied at room temperature. The results indicate that BM presents much higher strength, lower ductility and slightly higher HCF strength (107cycles, R=−1) than those of LM. Typical dislocation structures including straight prismatic slip lines, curved dislocation lines, dislocation tangles and twins can be discovered in fatigued specimens with two different microstructures. Primary α (αp) particles and secondary α (αs) lamellae accommodate more cyclic deformation than retained β (βr) laths. Grain boundary (GB) α layers have more effect on promoting crack initiation in LM than that in BM. As a result, fatigue microcracks mainly initiate at the interface between GB α films and prior β grains or at the αs/βr interphase for LM. However, microcracks primarily nucleate at the αp/βtrans (β transformed microstructure) interface or at αp particles in BM. The combination of transgranular and intergranular crack propagation could be observed in the two microstructures. Crack front profile of macrocrack in LM is rougher than that of BM during the stable propagation region.
TC25G alloy was heat treated at 950 °C/3 h, AC + 580 °C/6 h, AC and the bimodal structure with primary α phase + β transition structure was obtained. The creep properties of the alloy were tested in ...550–600 °C/150–250 MPa. The results show that the precipitations of silicide and α
2
phase is accompanied by the creep process. α
2
phase plays a dispersion strengthening role in both the primary and steady-state creep stages. However, in the accelerated creep stage, the mechanism of α
2
phase and dislocation changes from cutting mechanism to bypassing mechanism, and the strengthening effect is weakened. Silicide inhibits grain boundary slip mainly in the primary creep stage, and inhibits dislocation slip in the steady-state and accelerated creep stages. At 550 °C,
n
= 1.6 and
Q
= 280–371 kJ/mol (150–250 MPa) indicate that the creep of the alloy is a self-diffusion process, and the creep deformation is mainly controlled by dislocation slip. At 570–600 °C,
n
= 3.2 indicates that the dislocation climb controls the creep deformation. Meanwhile, compared with
Q
= 274 kJ/mol at low stress (150 MPa),
Q
= 365 kJ/mol at the high stress (200–250 MPa) indicates that the second phase precipitation enhancement is enhanced.
Graphical Abstract
The microstructure and room temperature tensile properties of heat-treated TC25G alloy after thermal exposure were investigated. The results show that the α
phase dispersed in the α phase, and ...silicide precipitated firstly at the α/β phase boundary and then at the dislocation of the α
phase and on the β phase. When thermal exposure was 0-10 h at 550 °C and 600 °C, the decrease of alloy strength was mainly due to the dominant effect of dislocations recovery. With the rise and extension of thermal exposure temperature and time, the increasing quantity and size of precipitates played an important role in the improvement of alloy strength. When thermal exposure temperature rose to 650 °C, the strength was always lower than that of heat-treated alloy. However, since the decreasing rate of solid solution strengthening was smaller than the increasing rate of dispersion strengthening, alloy still showed an increasing trend in the range of 5-100 h. When thermal exposure time was 100-500 h, the size of the α
phase increased from the critical value of 3 nm to 6 nm, and the interaction between the moving dislocations and the α
phase changed from the cutting mechanism to the by-pass mechanism (Orowan mechanism), and thus alloy strength decreased rapidly.
High-temperature titanium alloys are one of the most important research directions in the field of high-temperature aerospace alloys. They are mainly used in high-temperature-resistant components, ...such as blade disks, blades, and casings of aero-engines, and are key materials in a new generation of high thrust-to-weight ratio aero-engines. In the service environment of engineering applications, the creep resistance of high-temperature titanium alloys is one of the most important characteristic indicators. This paper reviews and analyzes the research status and progress on the creep properties of typical high-temperature titanium alloys in service in recent years. The effects of the creep parameters, alloy composition, and microstructure on the creep behavior of high-temperature titanium alloys are discussed, and various possible mechanisms for increasing the creep resistance of high-temperature titanium alloys are summarized.
Excellent mechanical properties combined with low density, good corrosion resistance and welding, make titanium alloy attractive structural materials for aerospace, ship navigation, weaponry and ...nuclear industry. However, the high cost impedes the further use of titanium alloy in different fields, and which is the key factor for productivity and further use of titanium alloy. Aiming at lost cost of titanium alloy, three parts of raw material, alloy design and working forming were overviewed, which will offer reference for how to low cost of titanium alloy.
The hot deformation behavior of Ti–22Al–25Nb was studied by the high temperature compression over a range of temperatures (950–1050 °C) and strain rates (0.001–10 s
−1
) in this paper. The ...work-hardening (WH) and softening deformation behaviors of Ti–22Al–25Nb were analyzed. Obvious linear decreasing regimes of WH rate curves can be found before the dynamic recrystallization (DRX) onset, which indicates WH + DRV (dynamic recovery) stage. And WH rate decreased significantly with strain rate reduced and temperature elevated. A physically-based constitutive model was established, which can well predict the flow behavior of Ti–22Al–25Nb. Additional, strain-rate sensitivity coefficient distribution map was established. The higher values of m appeared at the low strain rate. When the strain rate exceeded 0.1 s
−1
, the values of m were lower than 0.25.
Graphic Abstract
The phase composition before deformation is an important factor affecting the deformation mechanism of titanium alloy at room-temperature. In practical production, the initial phase composition can ...be greatly controlled by changing the solution cooling mode of the alloy, thus affecting the deformation mechanism and mechanical properties of the alloy to a certain extent. Therefore, the study of the effect of solution cooling rate on the deformation mechanism at room-temperature plays an important role in regulating the properties of the alloy. Through room-temperature compression experiments, the microstructure evolution and room-temperature plastic deformation mechanism of Ti–10Mo–1Fe near β-type alloys with different cooling rates after solution treatment at 870 °C were studied in this paper. The results show that the main room-temperature deformation mechanism of the Ti–10Mo–1Fe alloy under rapid cooling conditions (water-cooled) was the {332} twins and stress-induced orthorhombic martensite α″ phase. In addition, a few {112} twins were observed. The plastic deformation mechanism at room temperature under moderate cooling conditions (air-cooled) was primarily {332} twins and dislocation slip. Small numbers of {112} twins were also observed. Under slow cooling conditions (furnace cooling), no new phases are formed during the deformation process, and the plastic deformation mechanism at room temperature is dislocation slip.
The hot deformation behavior of a new Al-Mn-Sc alloy was investigated by hot compression conducted at temperatures from 330 to 490 °C and strain rates from 0.01 to 10 s
. The hot deformation behavior ...and microstructure of the alloy were significantly affected by the deformation temperatures and strain rates. The peak flow stress decreased with increasing deformation temperatures and decreasing strain rates. According to the hot deformation behavior, the constitutive equation was established to describe the steady flow stress, and a hot processing map at 0.4 strain was obtained based on the dynamic material model and the Prasad instability standard, which can be used to evaluate the hot workability of the alloy. The developed hot processing diagram showed that the instability was more likely to occur in the higher Zener-Hollomon parameter region, and the optimal processing range was determined as 420-475 °C and 0.01-0.022 s
, in which a stable flow and a higher power dissipation were achieved.
The ultra-fine grain Ti–6Al–4V alloy sheet was successfully achieved by friction stir processing (FSP). The low-temperature superplastic deformation mechanism of Ti–6Al–4V alloy under the strain rate ...of 3 × 10−4 s−1 at 600 °C was studied by scanning electron microscope, electron backscatter diffraction and superplastic tensile test. It is found that the grain size of Ti–6Al–4V alloy by FSP is refined from 7.48 μm to 0.82 μm, and there is no preferential crystallographic orientation of the uniform grain. After FSP, the β phase of the base material (BM) in the grain boundary is refined and homogenized. During the superplastic tensile processing, with the increase of strain, the grain is refined continuously, and the α→β phase transition is induced by the dislocations pile-up at the β grain boundary, and the content of β phase increases. The grain near the fracture was refined to 0.35 μm, and the stress concentration led to the formation of cavities near the β phase, which eventually caused the fracture. The dynamic recrystallization in superplastic tensile processing is mainly geometric dynamic recrystallization and discontinuous dynamic recrystallization. The elongation of superplastic tensile (1033%) is 19.7 times higher than that of BM (50%). The order of superplastic deformation mechanism in the low-temperature superplastic deformation of the ultra-fine grain Ti–6Al–4V alloy sheet is as follows: intragranular dislocation slip and diffusion, grain boundary sliding, and phase boundary sliding. Phase boundary sliding is the main deformation mechanism for low-temperature superplastic deformation.
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